The use of antennas on mobile platforms has grown dramatically with an increased demand by users to stay in touch in a more mobile society. This increased demand spans bidirectional exchange of data using mobile platforms for both personal and business needs. To meet this need, a moving platform, such as an automobile, boat, or airplane, typically uses an antenna that is able to track or “lock onto” a signal source, such as a satellite or terrestrial base station. In particular, phased array antennas with beam steering functionality often are used to provide this capability.
Phased array antennas typically use a number of phase shifters to vary the phase of radio frequency (RF) signals in a coordinated manner across the radiator elements of the antenna array to point the beam of the antenna in a desired direction. This type of beam steering can be used to track or lock onto a target regardless of the movement of the platform to which the antenna is attached. A phased array antenna is usually bidirectional, in that the beam of the antenna can be pointed to a target, such as a satellite, to both receive signals from and send signals to the satellite, or another component in the communication system. In other words, a phase shifter in a reciprocal antenna can facilitate full duplex communications in a mobile communication system.
For satellite communication (Satcom) systems, circular polarization (CP) is utilized, which usually requires a special CP forming network suitable for selected radiation elements. In the case of phased array antennas mounted on airplanes, referred to as aeronautical antennas, a number of design factors are important beyond the beam steering capability of the antenna.
For example, the phase shifters, as well as the CP forming networks, should be as small as possible, thus reducing the amount of space on a circuit board onto which they are mounted with other antenna components. Also, the phase shifters and CP forming networks should have the lowest possible insertion loss and minimal phase delay variation over a required frequency band. These and other design considerations are sometimes in conflict, making different configurations preferable for different applications depending on the importance of the various design considerations for the particular application. Phase shifters suitable for the applications described above are often connected in a series of stages, with a first course phase step followed by finer phase step phase shifter stages, to deliver desired phase shifts with a required resolution to each antenna element.